Sodium-sulfur ("Na/S") cells and batteries have a high specific energy and a high specific power, and are based on active materials which are relatively abundant and of low cost. They are rugged and reliable, and are used, for example, in applications such as satellites and electrically powered vehicles. The conventional sodium-sulfur cell is cylindrical in construction, with a cylindrical closed-end tube of solid electrolyte separating the cell cylinder into two annular chambers, one for anode material and one for cathode material. Another design is the voltaicpile design in which a flat conductive plate separates each cell and the solid electrolyte separates the anode chamber from the cathode chamber. In the flat plate design the sodium anode material and the sulfur cathode material are carried on inert porous conductive meshes, wools or pads, in electrode chambers that are separated by the solid electrolyte.
Sodium sulfur cells are operated at temperatures at which the sodium and sulfur are both liquid, typically about 300.degree. to 400.degree. C. In operation, sodium ions are transferred across the electrolyte, from the anode chamber to the cathode chamber during discharge. (In charging, Na+ ions are transported in the reverse direction, back to the anode chamber.) The material of choice for the ionically conductive electrolyte of a Na/S battery is so-called beta double prime alumina (b"-Al.sub.2 O.sub.3), which has Na+ ions in its crystal structure. In discharge, sodium ions from the anode material enter the crystal lattice of the beta alumina on the anode side of the electrolyte and displace other such ions from the cathode side, into the cathode chamber where they react with the sulfur to form sodium sulfide. Metallic sodium atoms do not move physically through the electrolyte from one side to the other, however, sodium ions are transferred across the electrolyte: as some ions enter on one side, others are released essentially simultaneously on the opposite side.